Drum brake modules of the type in question comprise an electromechanical actuator, which is secured on an outer side of the anchor plate, for driving a rotation-translation converter for converting a rotary drive motion into a translational actuating motion (B) of brake shoes, which are arranged on an inner side of the anchor plate, in a brake drum, said inner side facing away from the actuator, with the result that said shoes can perform an actuating motion in the direction of the brake drum, and wherein a lever-type expansion device is provided approximately centrally between the brake shoes, in particular for parking brake actuation.
A preassembled drum brake module having an expansion lever device (expansion lock), which locks when deenergized, including a spindle-nut mechanism on a rear side of an anchor plate for use in parking brake applications is known from DE 198 02 082 A1, which is incorporated by reference. Here, a force flow path is closed without losses since the expansion lever device is coupled directly to the electric motor and supported on the latter, and wherein the mechanism can contain rolling elements to increase efficiency. To ensure the required mobility when used with duo-servo brakes, the entire actuator subassembly is held flexibly on a rear side of a cover plate of the wheel brake. The system allows brake shoes of mirror-symmetrical design.
An electromechanically actuable duo-servo drum brake without control cable attachment is known from EP 594 233 B1, which is incorporated by reference. Here, an electric motor is arranged on a rear side of an anchor plate. The motor axis is arranged at right angles to an axis of rotation of a brake drum and drives a threaded spindle positioned rotatably and in an axially movable manner. The threaded spindle is provided parallel to the motor axis in the brake drum and is mounted in a housing. The threaded spindle is in engagement with an element which is mounted in an axially movable and non-rotatable manner in the housing and acts on a lever mechanism. In addition to an electric motor of relatively powerful construction, this design requires further components of very specific design and therefore does not permit simple variation in large-scale production.
In the case of particularly powerful drum brakes of the duo-servo parking-brake type, an expansion device serves to convert and distribute a translational stroke of an actuating element, which is imposed on the mechanism by the driver of the vehicle, for example, via a manually actuated brake lever or electromechanically via a central actuator (control-cable actuator), in such a way that two brake shoes are spread apart radially relative to one another with a corresponding force. As a consequence, the two brake shoes inevitably come into contact with a rotor (brake drum), and the braking forces are then introduced via a supporting block into an anchor plate fixed to the vehicle. Here, the expansion device is basically designed as a lever mechanism and comprises at least one rigid spring bridge of very high strength between the brake shoes, and an actuating lever, which is articulated thereto and on which an actuating element of the actuator system engages. DE 696 200 C1 and also DE 1 022 920 C1, which are incorporated by reference, in particular, disclose expansion devices of uniform stiffness which ensure, by purely structural means, that the lever mechanism cannot bend under the prevailing application forces. DE 10 2004 039 479 A1, which is incorporated by reference, also discloses that the expansion device/lever mechanism is to be designed to be as stiff as possible. An electromechanically actuable motor vehicle parking brake system with a conventional lever expansion mechanism in conjunction with a central or wheel-brake actuator system is disclosed by DE 41 29 919 A1, which is incorporated by reference.
WO2012/104395 A2, which is incorporated by reference, describes a drum brake module having an efficient, fixedly mounted wheel brake actuator having an integrated rotation-translation converter and no expansion lock. Thermal length changes in a drum brake can be compensated. For this purpose, an actuating lever is articulated at one end to one of the brake shoes, and wherein this actuating lever is coupled to an actuating element (control cable) of the actuator. This design requires special brake shoes.
WO 2009/030726 A1, which is incorporated by reference, discloses an electronic/slope-dependent application force adjustment system with an electronic control unit for the purpose of actuating an electromechanical duo-servo drum brake. Here, the expansion travel set is detected by the control unit by means of a travel sensor system, and the expansion device arranged within the drum incorporates the rotation-translation converter with the aid of a threaded nut/spindle arrangement and a spring energy storage device designed as a diaphragm spring pack. This spring energy storage device requires additional installation space.